The current firmware doesn't support to block VLAN. I saw a beta firmware in another post. You can try to update the beta firmware: https://community.tp-link.com/en/business/forum/topic/266112

If you need VLAN+QoS features, I think TL-SG108E is more appropriate because it has web interface to configure these feature, but TL-SG1005D doesn't have web interface. As for the power consumption,...

What's the specific issue? Can you still access the switch's web interface? If you can't access the web interface, you can try to upgrade the firmware via the Bootutil Menu:...

Oh, I found one thing that may be helpful! Those grayed-out Wi-Fi are all working on channel 11, while the one you are able to select is on channel 1. Maybe your Fritzbox needs to work on channel1....

You can try plugging cable modem into WAN1 and ADSL into WAN2 for a comparison test. And did you configure load balance or link backup? Try disabling them.

@EIBROG What type of VPN did you configure? You can check if other users that can connect to ER605. If other users can and there is no change on router's setting, you may still focus on the single...